This study aims to define techniques by which various subgroups of childhood hypertension can be categorized on the basis of plasma renin and plasma aldosterone profiling and the responses of plasma renin activity and plasma aldosterone to acute and chronic sodium depletion. Also, uric acid metabolism is being evaluated under basal conditions and following acute and chronic sodium depletion. To date we have evaluated 30 normotensive children and more than 75 children with various forms of childhood hypertension. We have been able to recognize children with increased renin activity as well as those with a suppressed response to acute volume depletion by criteria developed on the basis of evaluating normotensive children. Different subgroups of hypertensive children have had different responses of plasma renin activity and plasma aldosterone to acute and chronic volume depletion. Thirty to forty percent of the children with essential hypertension have had elevated levels of serum uric acid and a decreased fractional excretion of uric acid. A number of children with essential hypertension have also been shown to have an abnormal echocardiogram and an abnormal response to exercise. The data obtained in some of these children are being added to data already developed in a blood pressure tracking study entitled "Antecedents of Adolescent Hypertension."